Maddah, Layal . (2019-05). Guidelines for Systems of Barrier-Moment Slab Placed Over Steel and Geosynthetic MSE Walls and Subjected to Impact Levels Tl-3 Through Tl-5. Doctoral Dissertation.
Thesis
This dissertation presents design guidelines to design a roadside system against vehicle collision. The system is composed of a concrete roadside barrier anchored to a moment slab (barrier-moment slab or BMS) and placed over a Mechanically Stabilized Earth (MSE) wall that adopts steel or geosynthetic strip reinforcement. The guidelines cover three vehicle impact test levels: a 5,000 lb pickup truck, 22,000 lb single-unit truck and 79,300 lb tractor-van trailer crashing into the system at speeds of 62 mph, 56 mph, and 50 mph respectively. The test levels correspond to TL-3, TL-4, and TL-5 following AASHTO Manual for Assessing Safety Hardware. Developing design guidelines to design systems subject to vehicle impact required an evaluation of the overall performance of the system. Results from instrumented full-scale impact (crash) tests, previously carried out under projects NCHRP 22-20 (TL-3) and NCHRP 22-20(2) (TL-4 and TL-5) were used. TL-4 crash test was carried out as a part of this dissertation, and its findings are included herein and in NCHRP 22-20(2) report (submitted for review in June 2017). Finite Element (FE) simulations for the three tests were prepared using LS-DYNA software package, competent in transient dynamic analyses applications. The scope of the two previous studies was limited to MSE walls with steel reinforcement strips. In this dissertation, the guidelines are extended, for , for the first time, to include geosynthetic strip reinforcement. In the lack of full-scale crash testing, the simulations served as a powerful tool to unveil the behavior of geosynthetic systems. Auxiliary simulations were prepared to facilitate obtaining forces and displacements from the crash test simulations within 20% of those recorded in the full-scale crash tests. Vehicle impact into BMS system simulations (without the MSE wall) allowed the identification of controlling interface parameters. Results from reinforcement-soil interface simulations were compared with previous laboratory pullout tests to obtain pullout response that is representative of the actual response. This work ultimately resulted in comparable stresses and strains between the crash tests and the associated simulations for the three impact levels. These simulations were then used to explore the response of geosynthetic strips instead of steel strips.
